首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1048篇
  免费   14篇
电工技术   7篇
化学工业   108篇
金属工艺   13篇
机械仪表   12篇
建筑科学   15篇
矿业工程   8篇
能源动力   25篇
轻工业   131篇
水利工程   3篇
石油天然气   1篇
无线电   74篇
一般工业技术   106篇
冶金工业   444篇
原子能技术   8篇
自动化技术   107篇
  2021年   18篇
  2020年   11篇
  2019年   14篇
  2018年   5篇
  2017年   6篇
  2016年   9篇
  2015年   4篇
  2014年   9篇
  2013年   47篇
  2012年   12篇
  2011年   29篇
  2010年   20篇
  2009年   18篇
  2008年   17篇
  2007年   28篇
  2006年   24篇
  2005年   24篇
  2004年   26篇
  2003年   25篇
  2002年   15篇
  2001年   30篇
  2000年   20篇
  1999年   31篇
  1998年   114篇
  1997年   67篇
  1996年   48篇
  1995年   28篇
  1994年   31篇
  1993年   41篇
  1992年   22篇
  1991年   30篇
  1990年   15篇
  1989年   14篇
  1988年   18篇
  1987年   15篇
  1986年   11篇
  1985年   8篇
  1984年   14篇
  1983年   11篇
  1982年   11篇
  1981年   14篇
  1980年   16篇
  1979年   9篇
  1978年   7篇
  1977年   8篇
  1976年   22篇
  1975年   7篇
  1973年   7篇
  1968年   5篇
  1962年   3篇
排序方式: 共有1062条查询结果,搜索用时 15 毫秒
41.
42.
Heifers (n=10) were randomly selected from the slaughter line of a local factory each month for a period of 21 months. Rib steak (sampled at the 10th rib) from the left side of each carcass was taken for analysis. The cattle breeds selected during this study were Friesian, Hereford and Charolais. The mean weight of the left side for all carcasses was 146.6 (S.E.M.= 1.0kg). Graded carcasses selected for sampling during this trial were classified using the EUROP scale and the specific heifer grades chosen were factory grades EO4L and EO4H. Initial Hunter 'a' values (on the day of arrival in the laboratory) of rib steak from heifers finished between November and March (overwintered) were significantly (P<0.001) higher than Hunter 'a' values from heifers finished between April and October (pastured). After storage at 4?°C under simulated retail display conditions for 6 days, the Hunter 'a' values for overwintered samples were also significantly (P<0.001) greater than those for pastured samples. Breed also had an effect on the colour of the meat. After storage for 6 days, Hunter 'a' values of rib steak from Charolais were significantly (P<0.05) higher than either Friesian or Hereford. Pastured heifers had significantly (P<0.05) higher levels of the monounsaturated fatty acid C16.1 in the total lipid fraction of rib steak (neutral and polar) than samples taken from overwintered heifers. Pastured heifers had significantly (P<0.01) higher levels of the polyunsaturated fatty acid (PUFA) C18.3 in the phospholipid fraction than those from overwintered cattle. However, Hereford had significantly (P<0.05) higher levels of C14.0, C16.1 and C18.0 in the phospholipid fraction than those found in Friesian and Charolais. The level of α-tocopherol in the muscle was not affected by either pasturing/overwintering or breed. However, Continental breeds had significantly (P<0.05) higher levels of α-tocopherol in adipose tissue than Friesian.  相似文献   
43.
A hard problem in network testing is verifying the correctness of a class of networks, as well as the actual networks under test. In practice, at most a few networks (sometimes only one) are actually tested. Thus an important question is how to select one or more networks that are sufficiently representative to apply the results to a class of networks. We present a model-based technique for selecting a representative network. The central theorem establishes that the representative network displays any faults present in any network of the class. This paper introduces the concept of “self-similarity,” which is used to select the network, and presents the results of an experiment in testing one class of networks.  相似文献   
44.
This study investigated cross‐media credibility perception with respect to news coverage about the Iraq War. In an environment of political partisanship, perceptions of media credibility were likely affected by the audience’s political position on the war. Based on hostile media effect theory, a set of hypotheses was proposed to investigate whether the minority opinion group, war opponents, evaluated the Internet as a more credible medium than did neutrals or supporters. An online survey was conducted to which 481 people responded (71% war supporters, 19% opponents, 10% neutrals). Results showed that opponents of the war perceived the Internet as less aligned with a pro‐government position and as more credible than did neutrals or supporters. The opponent group also showed a strong negative correlation between perceived pro‐government alignment and perceptions of Internet credibility. For the minority partisan group, the diversity of information and views on the war was the main reason for the perception of high credibility of the Internet as a news channel.  相似文献   
45.
POTLIB 2001 is a computer program library of global chemical potential energy surface (PES) functions (91 functions in version 1.0) along with test data, a suite of utility programs, and a convenient user interface. The PES programs are written in ANSI standard FORTRAN77 and can be used to determine the Born-Oppenheimer potential energy of chemical systems as a function of the internal coordinates. The accompanying test data allow users to verify local implementations of this library. Finally, the utility programs permit use of this library in conjunction with a variety of chemical dynamics and chemical kinetics computer codes. Interface routines are provided for the POLYRATE and ABCRATE program packages of Truhlar and co-workers, the VENUS96 program package of Hase and co-workers, and the VARIFLEX program package of Klippenstein and co-workers; the routines in this library can also be used in conjunction with the DYNASOL program package of Zhang and co-workers. This article describes the library and the utility programs and outlines the systematic conventions used for interfaces in the computer programs contained in the library. Adherence to these conventions will allow future PESs to be compatible with this library.  相似文献   
46.
47.
48.
Landsat-D will be launched in late 1981 or early 1982 into a Sun-synchronous orbit near 700 km. Landsat-D systems and the principal observing instrument, the Thematic Mapper, are being designed and implemented to provide a significantly improved Earth-resources monitoring capability. The Thematic Mapper will have seven spectral bands (0.45-0.52, 0.52-0.60, 0.63-0.69, 0.76-0.90, 1.55-1.75, 2.08-2.35, and 10.5-12.5 ?m), with an instantaneous field of view at nadir of 30 m except for the thermal band (120 m). The data from the Thematic Mapper and other Landsat-D flight segment systems will be relayed to the Landsat-D ground data processing system using a direct readout capability or the Tracking and Data Relay Satellite System and communications satellites. The ground systems will process the data as it arrives at rates up to 100 Mbit/s and a total volume of 2.6 × 1011 bit/day into standard digital and photographic products within 48 hours of data acquisition. This includes 200 Multispectral Scanner Subsystem and 100 Thematic Mapper scenes per day. The Thematic Mapper increased spatial, spectral, and radiometric resolution should be of primary benefit in agricultural and vegetation surveys, but substantial improvements in resource and land cover observations for geology, land use, and water resources applications are also to be anticipated.  相似文献   
49.
50.
A model of computation is introduced which permits the analysis of both the time and space requirements of non-oblivious programs. Using this model, it is demonstrated that any algorithm for sorting n inputs which is based on comparisons of individual inputs requires time-space product proportional to n2.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号